The ability to control power is an important feature in modern work machines (e.g., fixed and mobile commercial machines, such as construction machines, fixed engine systems, marine-based machines, etc.). Today, modern machines control power through one or more control units, such as an Engine Control Unit (ECU). This unit includes hardware, software, and/or firmware that is used to manage various machine operations. For example, ECUs may be configured to control ignition and/or fuel injection operations to regulate power provided by the machine's engine.
An ECU performs these control functions by executing one or more programs stored in an internal memory. Typically, these programs include logic that produces one or more output values used as control signals by various components of a host machine. The program logic may access one or more performance maps to determine data values to produce the output values. A performance map is a data relationship between one or more control variables associated with operations of the host vehicle, such as ignition timing, engine RPM, etc. Each map may include one or more data values for each of many different operating conditions. For example, a performance map may include a relationship of data values (e.g., a mathematical function and corresponding data array) from which the program logic may obtain data values to produce an output signal.
Because ECUs may be implemented in different types of machines, a particular ECU may include several different performance maps corresponding to varying load conditions that may be experienced by the machine. Further, because machine applications and conditions vary, the performance maps may include different data values for customizing the machine's performance. Accordingly, modern machines may control power provided to a machine's drive train. Typically, however, these machines control machine power based on the speed of the engine, which has a direct affect on power losses due to, for instance, dissipated heat.
To illustrate these problems, FIG. 1 shows a graph of exemplary power curves associated with a conventional work machine. Curve 110 represents the power provided to the drive train by an engine of a conventional torque converter work machine in a first forward gear. Curve 115 represents the power provided by the drive train (torque converter output) in first forward gear to mechanisms used by the machine to travel on the ground, such as the power provided to the sprockets of a track type tractor work machine. Thus, curve 115 represent power that corresponds to the power provided to the work machine's drive train, as illustrated by curve 110. Similarly, curve 120 represents the power provided to the drive train in a second forward gear. Curve 125 represents the corresponding ground power provided by the machine's drive train based on the input power of curve 120. Curve 130 represents the power provided to the drive train in a third forward gear. And, curve 135 represents the corresponding power provided by the drive train based on the input power reflected by curve 130.
As shown, the power provided to the drive train in each of the three exemplary gears reaches maximum limits at certain ground speeds. For example, in first gear, the machine's engine produces high power at very low ground speeds and tapers after the machine reaches a certain speed (e.g., 1.5 mph). Also, the power produced by the machine's drive train follows pseudo-parabolic curves that reach peak levels based on the ground speed of the machine (e.g., “H” hp at 1.5 mph in first gear). As can be seen, the power loss at low speeds is very high due to the nature of a torque converter machine.
The typical working speed of a particular type of work machine also affects the power operations of the work machine. For example, if the typical working speed of a track type tractor work machine moving forward is 1.5 to 3.5 mph, the work machine would have to operate between first and second forward gears. The drive train power shown in FIG. 1; curves 115, 125, and 135 peaks at about “H” hp and then drops off, respectively. In this example, a constant drive train power of “H” hp would be ideal for this type of exemplary work machine. However, such operations are not feasible in machines that use gears and torque converters/dividers because of the significant power losses associated with operation of these components.
One typical machine designed to control a drive train is described in U.S. Pat. No. 6,434,466 (“the '466 patent”). The machine described in the '466 patent uses a transmission that transfers power produced by an engine to mechanisms that move the machine. The machine controls a drive train based on a plurality of information collected and determined by the machine. This information includes a desired wheel torque, engine speed, turbine speed, a selected gear and associated selected gear ratio, a transmission spin loss based on a first function of the turbine speed and the selected gear, a transmission torque proportional loss based on a second function of the turbine speed and the selected gear, a desired engine torque based on the transmission spin loss, the transmission torque proportional loss, and the selected gear ratio. Using this information, the drive train may control the actual wheel torque such that it approaches the desired wheel torque determined by the machine. Further, the '466 patent may use ground speed as an event threshold value that controls which method the vehicle may use to determine engine torque. For instance, the '466 patent determines engine torque using a power-based calculation if vehicle speed is above a predetermined threshold, and a gear ratio-based calculation if vehicle speed does not exceed the predetermined threshold.
Although modern machines, such as the one described in the '466 patent, have the ability to control a drive train based on the parameters associated with one or more machine components, they still experience power losses because of the machine transmission's dependency on engine speed. For example, at low ground speeds, a machine may experience significant power losses due to, for example, heat dissipated from the engine that is running at unnecessarily high speeds. Thus, the machine wastes power at these ground speeds because the machine is not moving, or moving very slow, while the engine is running at relatively high rpm. Also, there are no mechanisms in these machines to allow for ground travel control independent of engine machine operation.
Methods, systems, and articles of manufacture consistent with certain embodiments of the present invention are directed to solving one or more of the problems set forth above.